Look I'm a Nas/Wu/Mobb Deep head. But now it's about minimalism. You got to have slick lines while conveying your idea in as little words as possible.
As for 21, the guy has raw talent. He's not Lupe, but he has a unique style and voice. All he needs is to step up his bars just a little.
Listen to the third verse on Bank Account so you can hear what I'm hearing.
*Edit I just listened to it again. Yeah that shyt sounds hot. While everybody and their moms was doing the Migos flow, he came in the game with a new style to rock.